The present invention is directed to electrosurgical systems, apparatus and methods for removing an implanted object from a patient's body, and specifically to systems and methods for the removal of implanted endocardial or epicardial pacemaker leads or transvenous defibrillation leads from a patient's heart and the venous paths thereto.
Various types of pacemaker leads and their electrodes are introduced into different chambers of the heart, including the right ventricle, right atrial appendage, the atrium and the coronary sinus, although the majority of pacemaker leads are implanted in the right ventricle or appendage thereof. These flexible leads provide an electrical pathway between a pulse generator, connected to the proximal end of the lead, and the heart tissue, which is in contact with the distal end or electrode of the lead. Electrical pulses emitted by the pacemaker travel through the pacemaker lead and stimulate the heart to restore healthy heart rhythms for patient's whose hearts are beating irregularly.
Pacemaker leads usually comprise an insulating sleeve that contains a coiled conductor having an electrode tip at the distal end. This electrode tip is often placed in contact with the endocardial or myocardial tissue by passage through a venous access, such as the subclavian vein or one of its tributaries, which leads to the endocardial surface of the heart chambers. The electrode tip is held in place within the trabeculations of myocardial tissue. The distal ends of many available leads include flexible tines, wedges or finger-like projections which project radially outward to help prevent dislodgment of the lead tip from the cardial tissue.
Once an endocardial lead is implanted within a heart chamber, the body's reaction to its presence furthers its fixation within the heart. Shortly after placement, blood clots form about the flanges or tines due to enzymes released in response to the irritation of the cardial tissue caused by the electrode tip. Over time, fibrous scar tissue eventually forms over the distal end, usually in three to six months. In addition, fibrous scar tissue often forms, at least in part, over the insulator sleeve within the venous system and the heart chamber.
Endocardial leads occasionally malfunction, due to a variety of reasons, including lead block, insulation breaks, breakage of the inner helical coil conductor, etc. In addition, it is sometimes desirable to electronically stimulate different portions of the heart than that being stimulated with leads already in place. Due to these and other factors, a considerable number of patients may eventually have more than one, and sometimes as many as four or five, unused leads in their venous systems and heart. These unused leads often develop complications, such as infection, septicemia, or endocarditis. In addition, unused leads may entangle over time, thereby increasing the likelihood of blood clot formation, which may embolize to the lung and produce severe complications or even fatality. Further, the presence of unused leads in the venous pathway and inside the heart may cause considerable difficulty in the positioning and attachment of new endocardial leads in the heart.
Conventional techniques for removing unused pacemaker leads are also associated with serious risks. Standard mechanical traction and, more often, intravascular mechanical countertraction are the methods most commonly used at present (notably the system manufactured by Cook Pacemaker Corporation). External mechanical traction involves grasping the proximal end of the lead and pulling. This process is repeated daily, usually a few millimeters of the lead are removed from the patient each day, with progress monitored by chest radiography. Internal mechanical traction is accomplished by exerting traction (manual or sustained) on the lead via a snare, forceps or other retrieval catheter that has grasped the lead within the venous system. These techniques, however, can cause disruption of the heart wall prior to release of the affixed lead tip, causing fatality, or other complications, such as lead breakage with subsequent migration, myocardial avulsion or avulsion of a tricuspid valve leaflet. Moreover, lead removal may further be prevented by a channel of fibrotic scar tissue and endothelium surrounding the outer surface of the lead body or insulator sleeve at least part way along the venous pathway. Such channel scar tissue inhibits withdrawal of the lead because it is encased within the scar tissue. Continual pulling or twisting of the proximal free end of the lead could cause rupturing of the right atrial wall or right ventricular wall.
Intravascular countertraction is accomplished by applying traction on the lead while countering this traction by the circumference of dilator sheaths advanced over the lead. While maintaining sufficient traction on the lead to guide the sheaths, a pair of sheaths is advanced over the lead toward the myocardium to dislodge scar tissue from the lead. If insufficient tension is placed on the lead, however, the method is no longer countertraction but reduced to external traction with the aforementioned risks. In addition, misdirected countertraction along the lead body may tear the vein or heart wall.
In an effort to overcome some of the problems associated with mechanical traction and intravascular countertraction lead removal methods, lasers have been developed for extracting pacemaker leads. In some of these techniques, catheters having laser fibers at their distal end are advanced over the pacemaker lead to the site of attachment. The laser fibers are then energized to separate the lead from the fibrous scar tissue. These devices are described in U.S. Pat. Nos. 5,423,806, 5,643,251, 5,514,128 and 5,484,433. The standard laser light source for these devices is the xenon-chloride excimer laser, which is commercially available from Spectranetics Corporation of Colorado Springs, Col.
Conventional electrosurgery methods have not been successful in removing pacemaker leads. One of the factors which appears to create the greatest impediment to electrosurgical removal of pacemaker leads is scar tissue. Scar tissue exhibits much lower thermal conductivity and electrical conductivity than normal (e.g., myocardial) tissue. Since conventional electrosurgery generally relies on the conduction of electrical currents through the target tissue being cut or vaporized, conventional electrosurgery has failed to remove this scar tissue. In fact, previous attempts to use conventional electrosurgery methods to remove pacemaker leads have resulted in current flow and thermal effects in the "healthy" tissue surrounding the scar tissue mass, but not in the scar tissue mass itself. As a result, the targeted scar tissue was not affected and the lead was not removable.